According to Peacocke, concepts are individuated by their possession conditions, which are specified in terms of conditions in which certain propositions containing those concepts are believed. In support, Peacocke tries to explain what it is for a thought to have a structure and what it is for a belief to have a propositional content. I show that the possession condition theory cannot answer such fundamental questions. Peacocke’s theory founders because concepts are metaphysically fundamental. They individuate the propositions and thoughts containing them, which in turn individuate the propositional attitudes that are relations to those propositions or thoughts.